This project will conduct a detailed techno-economic feasibility analysis to identify fossil-free, cost-effective, resilient, and robust technology options that serve simultaneous heating and cooling requirements of co-located buildings, and that are applicable for a range of Department of Defense (DoD) sites. This project will analyze a thermal reservoir network; a thermal microgrid that uses a water distribution loop that operates at near-ambient temperature. This distribution loop will be coupled to local environment thermal sources, sinks and storage, and to energy transfer stations with reversible heat pumps that are located in the buildings. The design will improve energy resilience through load shifting and controlled dispatch of technology. This project will demonstrate annual system-level performance through simulations, targeting a seasonal performance factor of 6-8, a 20-30% peak load shaving and 50% power reduction over resilience events, with life cycle costs under $0.20/kWh. The thermal reservoir network is modularly expandable. This allows DoD to build these systems in a phased approach as capital becomes available, and customize them to different sites using various technologies for storage and renewable integration.

This project will conduct a techno-economic feasibility analysis of pareto-optimal archetypical configurations that show the wide applicability of the energy concept. This project will deliver a conceptual energy and control system design with quantified energy, power, resilience, and cost savings, and with guidance for extending the design to other sites. The innovation in the approach is three-fold. First, thermal reservoir networks provide heating and cooling at very high efficiency due to 1) geothermal coupling with the ground and/or local bodies of water serving as heat sources and sinks, 2) use of low-temperature waste heat from one building to serve another’s loads, and 3) the potential for modularly integrating renewables and a variety of storage technologies. The system control will allow shifting loads in time and among energy carriers to provide peak load shaving and power reduction over resilience events. Second, thermal reservoir networks can be modularly expanded, allowing phased investment and high customization to other sites. Third, novel Modelica technologies that the team spearheaded will be used to design and analyze the energy systems, as conventional load-based simulations lack the models and mathematics needed to express controls and piping networks that are central to the performance and robustness of fifth generation district energy systems. The Modelica-based approach allows rapid modeling and testing of actual advanced control sequences, and export of models as digital twins to support implementation, commissioning and operation using open standards. These benefits reduce the risks associated with deploying a system for which not much design and installation experience exist in the U.S. The modeling approach will help ensure that the design intent is realized and the system operates as expected.

Compared to state-of-the-art district energy systems, thermal reservoir networks 1) reduce trenching and distribution costs through use of one, non-insulated pipe, 2) reduce capital costs and allow phased buildout through modular extension of the system with lower capacity requirements for central equipment, and 3) reduce energy costs and greenhouse gas emissions by use of low grade waste heat and environmental sources and sinks. The modular form of the reservoir network makes it applicable to other DoD sites: generation and storage that can be tailored to different load profiles, and installations that can be modularly extended as capital becomes available, thereby avoiding costs of large central plants.